Process for the preparation of molybdenum metal



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This invention relates to a novel process for the preparation of molybdenum metal and salt complexes of said metal. More particularly, the invention pertains to a method for directly preparing molybdenum and salt complexes from available molybdenum-containing minerals.

This application is a division of Serial No. 848,891, filed October 27, 1959, now US. Patent No. 3,053,614.

Molybdenite, M08 is the only molybdenum mineral of significant commercial importance. This mineral, which constitutes about 0.2-1.0% of the ore deposit, is contaminated with large quantities of quartz, and lesser amounts of pyrites, FeS, and chalcopyrite, CuFeS It is recovered commercially from the ore by a process comprising grinding to minus 200 mesh, classification and selective flotation. Recovery of molybdenite in excess of 93% is accomplished by the use of a pine oil ester, alone or in the presence of a hydrocarbon and/or a wetting agent, as the flotation material. Sodium cyanide is used as an inhibiting agent to control the pyrites and chalcopyrite levels in the product. Alkaline reagents such as lime or soda ash are employed to prevent flotation of other iron salts. Composition ranges for com mercial molybdenite concentrates are as follows.

TABLE I Component: Percentages Mo 50-54 S 34-89 Mo oxides 0.05 SiO 1-10 A1 0.5-2 CrO 0.03 MgO 0.04 Pb 0.06 Cu 0.1-0.3

In the present commercial methods for production of molybdenum metal, the molybdenite is converted to M00 by burning in a Herreshotf furnace at about 1100 F. with simultaneous evolution of sulphur dioxide. Since M00 is quite volatile at 1300 F. and melts at about 1460 F., close temperature control is required to prevent excessive volatilization losses and serious operating problems, such as wear and corrosion of the rabble teeth, plugging of exit holes, hardening of the bed, etc.

The resulting M00 concentrate is then upgraded either by chemical processes or by volatilization. In the latter method, the M00 is fed as a thin layer on a sand hearth or a furnace operated at 1200 C. Since M00 volatilizes above 600 C., it is transferred from the furnace chamber through furnace ports to a sublimer by an air sweep. Although this M00 is of high purity, the yields are only in the range of about 60 to 70%. Upgrading of the M00 concentrates by the chemical method involves aqueous alkaline treatment, utilizing such chemicals as Na CO (NH CO or NH OH, under pressure and followed by controlled acidification to precipitate purified M00 hydrate or ammonium molybdate. Yields are slightly 3,146,093 Patented Aug. 25, 1964 higher in this method because various liquors can be conveniently recycled, but it is obvious the method is expensive and time consuming.

Molybdenum metal powder is prepared from the M00 by a high temperature, two stage hydrogen reduction method:

Stage 1 GOO-700 C. M00 H: M002 2 Stage 2 950-1100 O. M002 2113 M0 2HzO Stage 1 is carried out at about 600 C. because M00 is volatile above this temperature. If a one step reaction were carried out, the by-product steam would reach a high concentration and would tend to reverse the reaction by combining with the molybdenum. It has also been reported that high concentrations of Water in the overhead vapors lead to the formation of coarse molybdenum powder, which would be unacceptable in certain powder metallurgical processes. Furthermore, the temperature, time and hydrogen flow rates must be closely controlled to produce powder having the desired state of subdivision. It is also apparent that operations at temperatures of about 1000 C. in a hydrogen, steam, and oxygencontaining atmosphere cause serious problems with respect to materials of construction. A safety hazard also results from the presence of finely divided molybdenum.

It was also found that, despite the high temperature second reduction step, all of the oxygen-bearing compounds are not removed. Consequently, sintering of compressed molybdenum bars at 1600 to 2200 C. is employed to complete the removal of the oxygen-containing compounds and to give a material suitable for conversion to mill products. This sintering treatment also removes most of the hydrogen which contaminates the molybdenum powder. The complexity and numerous disadvantages of this prior art method has intensified efforts to devise more satisfactory processes.

A recently disclosed process for preparing molybdenum metal is disclosed in US. Patent No. 2,834,671, issued to Nachtman and Poole. Although this process involves the direct reduction of M08 with tin, temperatures of at least 1200 C. are required.

One object of this invention is to provide a process for the production of molybdenum metal which avoids the disadvantages of the prior art method. Another object of this invention is to provide a molybdenum metal process which does not require the elevated temperatures prescribed by the prior art processes. A further object of this invention is to provide a method for preparing molybdenum salt complexes. Other objects of this invention will become apparent from the ensuing description.

In accordance with the present invention, it has now been found that molybdenum metal may be effectively produced from molybdenite by directed reduction with sodium metal. The reaction is preferably carried out in a solid alkali metal halide, e.g. sodium chloride, reaction medium. In general, the molybdenite is diluted with sodium chloride, for example, and then admixed with the sodium metal. It is preferred to employ moisture-free molybdenite, and to maintain an atmosphere of inert gas throughout the processing steps of this invention which utilize heat. Conventional inert gases such as helium, argon, etc., and mixtures thereof are employed. The reduction of the molybdenite to the metal may be carried out in one step, i.e., by adding substantially stoichiometric amounts of sodium to reaction mixture, or in several stages by carefully controlled addition of the sodium reductant. The use of solid particles of an alkali metal halide is preferred since it permits better control over the reaction heat and insures the production of a more uniform molybdenum metal powder product. Furthermore, a reduction product, MoS-Na S, results, and its preparation constitutes one important feature of this invention. The intermediate product will be referred to throughout this specification and claims as a molybdenum salt complex. This salt complex may be employed as a high energy catalyst for polymerization reactions, alkyl reforming, etc., and as a lubricant.

In order to more specifically describe the invention, it will be described below with particular emphasis on the two stage reduction process. The amount of sodium employed in the first stage will range from about 40 to 75%, and preferably about 45 to 65%, the amount stoichiometrically required to reduce the M08 completely to molybdenum metal. The reaction taking place is as follows:

TABLE II Reduction Temp. C.) Time Run No. NaCl/MOS; (Mills) Initial Max.

Mild agitation was employed during these runs to insure complete contact of the reactants. Although the use of a sodium chloride reaction medium or diluent is preferred, as stated above, it is possible to carry out the desired reductionwith'out this material. For example, the reaction' could b'e-performed in a continuous manner with control over the reaction temperature by adding incremental amounts of sodium.

It will also be understood that other alkali metals such as potassium and lithium may also be employed as the reductant'. The use of sodium is, however, preferred.

The product from the first reaction stage is cooled, and recovered as such or treated further to produce molybdenum metal. The latter procedure involves mixing the product mixture with the additional amount of sodium required to complete the" reduction. This reaction is carried out at a temperature within the range of about 100 to 900 C., preferably about'300 to 700 C. Ordinarily, the reduction will be completed within 3 minutes. The reaction which occurs is as follows:

manner, it is possible to utilize the heat of reaction, resulting from completion of the molybdenum sulfide reduction, in bringing the spalt mixture up to a 'sintering temperature. 7

Obviously important economic advantages 4 would result by utilizing this type of operation on a commercial scale.

The sintered reaction product mixture is cooled to room temperature, crushed preferably to a size of about minus 10 mesh, and leached. In general, an aqueous acidic leach solution having a pH within the range of about 2 to 10, preferably 3 to 6, will be employed for this purpose. The acid may be mineral acids such as hydrochloric, sulfuric, nitric, and mixtures thereof. The use of hydrochloric acid is preferred. At high acidities, the molybdenum powder has a tendency to react with the leach solution to form insoluble oxides. At high alkalinity, on the other hand, any impurities which may be present tend to precipitate and the molybdenum is slowly dissolved. The spalt product is leached until it is free of by-product sodium sulfide and sodium chloride diluent, if the latter is employed. It was also found that this leaching technique also lowered iron, nickel, cobalt, copper, silicon, aluminum, and zinc contamination. The resulting molybdenum metal product is grayish-black in color and has an average particle size of less than about 10 mesh, generally about 30 to 200 mesh.

The invention will be more fully understood by reference to the following illustrative examples:

EXAMPLE I To 50.0 grams of dry M08 was added 200 grams of dry NaCl and the mixture placed in the reduction vessel. An argon sweep was initiated and maintained throughout the reduction. After dicing 15 grams of sodium, it was added to the NaCl-M0S mixture. The temperature of the reactants was raised to C. where agitation was initiated. Reduction began at C. to give a maximum temperature increase of 87 C. Reaction was completed, as indicated by heat evolution, in 2.9 minutes. Agitation was discontinued, the spalt cooled to room temperature and then removed from the reactor under an inert atmosphere. Upon exposure to moist air, slow reaction was noted. This experiment shows that non-molten, high surface MoS-Na S complex is reactive in air.

EXAMPLE II To 100 grams of synthetic M05 was added 200 grams of NaCl. After placing the mixture in the reducer and establishing an argon atmosphere, it was heated to 225 C. for several hours with agitation to expel moisture. After cooling to room temperature, 29 grams of sodium was charged to the reducer and the mixture heated to 90 C. Agitation was again started with the reduction at 92 C. to give a maximum temperature of 390 C. in 1.65 minutes. The reaction mixture was heated to 710 C. where agitation became diflicult indicating incipient melting. At 815 C. agitation was carried out with ease thus indicating complete melting of the complex-NaCl mixture. After heating for about one hour, the MoS-Na s complex was cooled to room temperature and removed from the reducer as in Example I. The spalt upon exposure to air was inert, thus indicating a lower energy and surface area product was obtained.

EXAMPLE III The procedure of Example II was carried out except that an additional 29 grams of sodium was added to the MOS-Na S complex before heating to 710 C. After sintering at 800 C. for four hours, the spalt was cooled to room temperature and removed from the reducer. No reaction with moist air was noted. The spalt wa crushed to minus 10 mesh and leached with aqueous HCl solution maintained at a pH of 4-6, until the Na S and NaCl had been solubilized. The resulting molybdenum powder was 90 percent minus 100 mesh and weighed 53 grams, thus indicating an 88 percent yield by weight. Three are melts of the powder gave an ingot with a Brinnel Hardness Number of (1500 kg. load).

The above data show that the process of this invention may be effectively employed to produce molybdenum metal or molybdenum salt complexes directly from molybdenum-containing minerals such as molybdenite or molybdenum trisulfide.

While particular embodiments of this invention are shown above, it will be understood that the invention is obviously subject to various modifications without departing from its broader aspects.

What is claimed is:

1. A method for the preparation of molybdenum metal which consists of reacting at a temperature of about 100 to 900 C. a molybdenum sulfide-sodium sulfide complex with an amount of alkali metal suflicient to reduce said molybdenum sulfide-sodium sulfide complex to molybdenum metal and recovering said molybdenum metal.

2. The method of claim 1 wherein said temperature is about 300 to 700 C.

3. The method of claim 1 wherein said alkali metal is sodium.

4. The method of claim 1 wherein said molybdenum metal is leached with a mineral acid.

5. The method of claim 4 wherein said mineral acid is hydrochloric acid.

6. A method for the preparation of molybdenum metal which consists of reacting at a temperature of about 100 to 900 C. a molybdenum sulfide-sodium sulfide complex with an amount of alkali metal sufficient to reduce said molybdenum sulfide-sodium sulfide complex to molybdenum metal, heating the resulting reaction product mixture at a sintering temperature of about 600 to 900 C. for a period of at least 1 hour, and recovering said molybdenum metal product.

7. The method of claim 6 wherein said reaction temperature is about 300 to 700 C. and said sintering temperature is about 750 to 850 C.

8. The method of claim 6 wherein said alkali metal is sodium.

9. The method of claim 6 wherein said molybdenum metal product is leached with a mineral acid.

10. The method of claim 9 wherein said mineral acid is hydrochloric acid.

References Cited in the file of this patent UNITED STATES PATENTS 835,052 Becket Nov. 6, 1906 1,602,527 Gero Oct. 12, 1926 3,020,151 Nachtman et al. Feb. 6, 1962 

1. A METHOD FOR THE PREPARATION OF MOLYBDENUM METAL WHICH CONSISTS OF REACTING AT A TEMPERATURE OF ABOUT 100* TO 900*C. A MOLYBDENUM SULFIDE-SODIUM SULFIDE COMPLEX WITH AN AMOUNT OF ALKALI METAL SUFFICIENT TO REDUCE SAID MOLYBDENUM SULFIDE-SODIUM SULFIDE COMPLEX TO MOLYBDENUM METAL AND RECOVERING SAID MOLYBDENUM METAL. 